Home | History | Annotate | Download | only in CodeGen 
      1 //===-- StackMapLivenessAnalysis.cpp - StackMap live Out Analysis ----------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file implements the StackMap Liveness analysis pass. The pass calculates
     11 // the liveness for each basic block in a function and attaches the register
     12 // live-out information to a stackmap or patchpoint intrinsic if present.
     13 //
     14 //===----------------------------------------------------------------------===//
     15 
     16 #include "llvm/ADT/Statistic.h"
     17 #include "llvm/CodeGen/LivePhysRegs.h"
     18 #include "llvm/CodeGen/MachineFrameInfo.h"
     19 #include "llvm/CodeGen/MachineFunction.h"
     20 #include "llvm/CodeGen/MachineFunctionAnalysis.h"
     21 #include "llvm/CodeGen/MachineFunctionPass.h"
     22 #include "llvm/CodeGen/Passes.h"
     23 #include "llvm/Support/CommandLine.h"
     24 #include "llvm/Support/Debug.h"
     25 #include "llvm/Support/raw_ostream.h"
     26 #include "llvm/Target/TargetSubtargetInfo.h"
     27 
     28 using namespace llvm;
     29 
     30 #define DEBUG_TYPE "stackmaps"
     31 
     32 static cl::opt<bool> EnablePatchPointLiveness(
     33     "enable-patchpoint-liveness", cl::Hidden, cl::init(true),
     34     cl::desc("Enable PatchPoint Liveness Analysis Pass"));
     35 
     36 STATISTIC(NumStackMapFuncVisited, "Number of functions visited");
     37 STATISTIC(NumStackMapFuncSkipped, "Number of functions skipped");
     38 STATISTIC(NumBBsVisited,          "Number of basic blocks visited");
     39 STATISTIC(NumBBsHaveNoStackmap,   "Number of basic blocks with no stackmap");
     40 STATISTIC(NumStackMaps,           "Number of StackMaps visited");
     41 
     42 namespace {
     43 /// \brief This pass calculates the liveness information for each basic block in
     44 /// a function and attaches the register live-out information to a patchpoint
     45 /// intrinsic if present.
     46 ///
     47 /// This pass can be disabled via the -enable-patchpoint-liveness=false flag.
     48 /// The pass skips functions that don't have any patchpoint intrinsics. The
     49 /// information provided by this pass is optional and not required by the
     50 /// aformentioned intrinsic to function.
     51 class StackMapLiveness : public MachineFunctionPass {
     52   const TargetRegisterInfo *TRI;
     53   LivePhysRegs LiveRegs;
     54 
     55 public:
     56   static char ID;
     57 
     58   /// \brief Default construct and initialize the pass.
     59   StackMapLiveness();
     60 
     61   /// \brief Tell the pass manager which passes we depend on and what
     62   /// information we preserve.
     63   void getAnalysisUsage(AnalysisUsage &AU) const override;
     64 
     65   MachineFunctionProperties getRequiredProperties() const override {
     66     return MachineFunctionProperties().set(
     67         MachineFunctionProperties::Property::AllVRegsAllocated);
     68   }
     69 
     70   /// \brief Calculate the liveness information for the given machine function.
     71   bool runOnMachineFunction(MachineFunction &MF) override;
     72 
     73 private:
     74   /// \brief Performs the actual liveness calculation for the function.
     75   bool calculateLiveness(MachineFunction &MF);
     76 
     77   /// \brief Add the current register live set to the instruction.
     78   void addLiveOutSetToMI(MachineFunction &MF, MachineInstr &MI);
     79 
     80   /// \brief Create a register mask and initialize it with the registers from
     81   /// the register live set.
     82   uint32_t *createRegisterMask(MachineFunction &MF) const;
     83 };
     84 } // namespace
     85 
     86 char StackMapLiveness::ID = 0;
     87 char &llvm::StackMapLivenessID = StackMapLiveness::ID;
     88 INITIALIZE_PASS(StackMapLiveness, "stackmap-liveness",
     89                 "StackMap Liveness Analysis", false, false)
     90 
     91 /// Default construct and initialize the pass.
     92 StackMapLiveness::StackMapLiveness() : MachineFunctionPass(ID) {
     93   initializeStackMapLivenessPass(*PassRegistry::getPassRegistry());
     94 }
     95 
     96 /// Tell the pass manager which passes we depend on and what information we
     97 /// preserve.
     98 void StackMapLiveness::getAnalysisUsage(AnalysisUsage &AU) const {
     99   // We preserve all information.
    100   AU.setPreservesAll();
    101   AU.setPreservesCFG();
    102   MachineFunctionPass::getAnalysisUsage(AU);
    103 }
    104 
    105 /// Calculate the liveness information for the given machine function.
    106 bool StackMapLiveness::runOnMachineFunction(MachineFunction &MF) {
    107   if (!EnablePatchPointLiveness)
    108     return false;
    109 
    110   DEBUG(dbgs() << "********** COMPUTING STACKMAP LIVENESS: " << MF.getName()
    111                << " **********\n");
    112   TRI = MF.getSubtarget().getRegisterInfo();
    113   ++NumStackMapFuncVisited;
    114 
    115   // Skip this function if there are no patchpoints to process.
    116   if (!MF.getFrameInfo()->hasPatchPoint()) {
    117     ++NumStackMapFuncSkipped;
    118     return false;
    119   }
    120   return calculateLiveness(MF);
    121 }
    122 
    123 /// Performs the actual liveness calculation for the function.
    124 bool StackMapLiveness::calculateLiveness(MachineFunction &MF) {
    125   bool HasChanged = false;
    126   // For all basic blocks in the function.
    127   for (auto &MBB : MF) {
    128     DEBUG(dbgs() << "****** BB " << MBB.getName() << " ******\n");
    129     LiveRegs.init(TRI);
    130     // FIXME: This should probably be addLiveOuts().
    131     LiveRegs.addLiveOutsNoPristines(MBB);
    132     bool HasStackMap = false;
    133     // Reverse iterate over all instructions and add the current live register
    134     // set to an instruction if we encounter a patchpoint instruction.
    135     for (auto I = MBB.rbegin(), E = MBB.rend(); I != E; ++I) {
    136       if (I->getOpcode() == TargetOpcode::PATCHPOINT) {
    137         addLiveOutSetToMI(MF, *I);
    138         HasChanged = true;
    139         HasStackMap = true;
    140         ++NumStackMaps;
    141       }
    142       DEBUG(dbgs() << "   " << LiveRegs << "   " << *I);
    143       LiveRegs.stepBackward(*I);
    144     }
    145     ++NumBBsVisited;
    146     if (!HasStackMap)
    147       ++NumBBsHaveNoStackmap;
    148   }
    149   return HasChanged;
    150 }
    151 
    152 /// Add the current register live set to the instruction.
    153 void StackMapLiveness::addLiveOutSetToMI(MachineFunction &MF,
    154                                          MachineInstr &MI) {
    155   uint32_t *Mask = createRegisterMask(MF);
    156   MachineOperand MO = MachineOperand::CreateRegLiveOut(Mask);
    157   MI.addOperand(MF, MO);
    158 }
    159 
    160 /// Create a register mask and initialize it with the registers from the
    161 /// register live set.
    162 uint32_t *StackMapLiveness::createRegisterMask(MachineFunction &MF) const {
    163   // The mask is owned and cleaned up by the Machine Function.
    164   uint32_t *Mask = MF.allocateRegisterMask(TRI->getNumRegs());
    165   for (auto Reg : LiveRegs)
    166     Mask[Reg / 32] |= 1U << (Reg % 32);
    167 
    168   // Give the target a chance to adjust the mask.
    169   TRI->adjustStackMapLiveOutMask(Mask);
    170 
    171   return Mask;
    172 }
    173